1. Field of the Invention
This invention relates to industrial presence sensor systems and, more specifically, to cable motion detection systems.
2. Related Art
High volume manufacturing processes move large numbers of production units through manufacturing lines. One example of such a process is baked goods. High numbers of loaves of bread are processed in a manufacturing plant. These loaves are transported by conveyor belt from operation to operation. During transportation, for various reasons such as jamming an error will occur and the loaves will fall off the conveyor belt. Alternatively, empty bread pans may jam. Empty bread pans are cooled off on long conveyors before coming back to be reused. When these bread pans jam, the bread pans become damaged from falling off the conveyor or from hitting each other and must be replaced. Alternatively, the pans jam machinery (equipment), damaging the equipment such that it must be repaired or replaced. If the problem is not corrected quickly, or if the manufacturing line is not stopped quickly, a great number of loaves of bread and/or bread pans will fall on the floor or jam equipment. These loaves and damaged bread pans must then be discarded, while the equipment can require repair or replacement. This results in higher manufacturing costs.
Because these lost bread pans are considered pure waste and because a very large number of bread pans (and loaves) can be lost, it is critical that any falling bread pans be identified as quickly as possible. Accordingly, one means of identifying conditions when bread pans are falling is to add alarms at trouble points, instruct the existing employees to watch for the alarms in addition to their regular duties. However, any losses from the failure to recognize alarms are simply absorbed. Thus, it is a forgone conclusion that a loss will occur, and the major challenge is managing the extent of the loss.
Though the above example relates to the bakery process, the illustrated problem is common to many high volume manufacturing processes.
Accordingly, there is a need in the art to provide a system which will enable an automatic means for monitoring the status of the material involved in the manufacturing processes.
An optical emitter/detector pair system produces a long beam that is interrupted whenever an object moves between the emitter and the detector. These systems are difficult to align and keep aligned. In addition, once in place, the beams are not visually apparent and thus individuals who are moving may walk between the emitter and detector, setting off false alarms. Further, optical sensors have difficulty with wet, dusty, hot, corrosive or otherwise extreme conditions. An area of particular difficulty for optical sensors is transparent targets, many of which cannot be reliably detected using common light sources. Moreover, because optical sensors are practically limited to line-of-sight beams, an array of detectors and emitters must be utilized if it is desired to detect an object crossing anywhere through a plane in space. Theoretically, mirrors may be used to expand the area of coverage, but alignment, signal strength, environmental factors, and maintenance issues make the use of mirrors less attractive.
In certain instances, information regarding the status of the manufacturing process may be determined by obtaining information on the speed of the conveyor belt. If the conveyor belt is jammed, the speed may be zero, and a problem arises. U.S. Pat. No. 3,743,913 issued to Rebucci discloses a mechanism for electrically transmitting the speed of a conveyor belt. However, if a problem such a jamming occurs which may cause manufactured articles to fall off the conveyor belt the belt speed is not affected, and no information is developed. Vehicle speed detectors which provide an alarm for excessive speed generally are of course well known in the art, as in U.S. Pat. Nos. 3,648,267, and 3,859,629.
U.S. Pat. No. 3,838,341 issued to Gaines discloses a detection system for determining unacceptable deviations from a desired spacing pattern in the passage of articles past a station. This solution is limited to checking the status at only one point. If multiple points are needed, multiple devices are required. Also, an entire area cannot be checked, given the constraint that only the status of a particular point can be checked. In addition, the existence of a desired spacing pattern is a prerequisite of such a detection system, while such a spacing pattern in fact does not exist for many production lines.
Wire-type sensors and detectors for determining the presence of various articles are also known. For example, U.S. Pat. No. 4,367,459 discloses a taut wire intrusion detection system in which an actuator is connected to a group of tensioned wires. A force transducer outputs an electrical signal proportional to the force applied to the actuator; when the force exceeds a predetermined threshold, an alarm is activated.
In another example, U.S. Pat. No. 4,736,194 discloses a fence with security wires fastened to posts via sensors. An alarm signal is generated when only one or only a few security wires move slowly. However, these slow movements are ignored when caused by environmental factors such as changes in temperatures and wind forces because the signal amplitudes of the sensors are drawn up to a mean value and only threshold deviations from the mean value create an alarm situation. One mode compares the tension of one wire with the average tension of a group of wires to ignore slow noise sources. Another mode compares the time rate of change of wire tension to a threshold value. This reference does not teach or suggest the use of time rate of change of position.
In yet another example, U.S. Pat. No. 4,929,926 discloses an intrusion detection barrier utilizing a coiled wire fence and a sensor wire tensioned between a pair of ground wires. The sensor wire, which is connected to an intrusion detector, is free to move along its longitudinal axis, but is not free to move transversely. The intrusion detector may be of the force sensing type or of the pull switch type.
Similarly, U.S. Pat. No. 5,371,488 discloses a tension sensing security apparatus which senses variation in the longitudinal tension in taut wire and produces a tension signal which is transmitted to a central monitoring location. While in the general area of cable tension transducers, none of these references teach or suggest applications of the technology to the area of high volume manufacturing processes. The general class of cable pull switches (an industrial product often used to trigger manual safety alarms) suffer from significant limitations: they are not very sensitive; they are limited in cable length to around 100 feet; they do not move out of the way of an object; and they can be deactivated by mechanical failures.
U.S. Pat. No. 5,236,144 discloses a cable extension linear position transducer which has an integrated support structure, a potentiometer having a shaft, a drum affixed to the shaft and a tension spring. This type of transducer has been used in conjunction with industrial limit alarms to signal when an absolute limit has been reached. However, these applications rely on the inherent accuracy and repeatability of these precision instruments, and do not adaptively filter out the noise sources that more strongly affect longer, lower stiffness cables or lines. Precise measurement of the linear movement of an item is provided by this invention, but no other applications of this technology in other arts are either taught or suggested.
U.S. Pat. No. 3,882,474 discloses a system for monitoring the instantaneous velocity of a pipe string being tripped relative to a well bore. Specifically, the invention discloses a unit which derives an electrical signal as a function of instantaneous pipe speed, and a monitoring system which compares signals representative of instantaneous velocities and provides an alarm when predetermined velocity limits are exceeded. There is no automatic adaptation to changing conditions disclosed or suggested by this reference.
U.S. Pat. No. 4,128,888 discloses a velocity control system for an oil drilling rig which gathers information on certain indices and compares that information against certain predetermined threshold values. If certain values are exceeded, output signals or alarm signals are generated. The information gathered is of actual velocity and direction of travel, and the predetermined thresholds relate to minimum and maximum velocities, and direction of travel. Output signals are generated when the actual velocity is not within the minimum and maximum thresholds, or when the direction of travel deviates from the predetermined direction of travel.